It is known to form a filter stack for a filter press which is composed of a plurality of filter plates which are disposed beside one another in pairs. Filter chambers are in each case formed between the filter plates. To this end, the filter plates display a central filter face and a thicker sealing periphery which frames the central filter face. The filter plates in the filter press can be displaced away from and toward one another, by way of which the filter chambers can be opened and closed.
Each filter chamber typically displays at least one inlet and one outlet. The suspension to be filtered which is typically referred to as sludge, flows via the inlet into the filter chamber. The suspension is then filtered by means of a filter cloth, wherein the solid matter is retained by the filter cloth in the filter chamber, such that a so-called filter cake is created. The filtrate which has been freed from the particulate matter is then conducted via the outlet out of the filter chamber.
In order to reduce the residual humidity in the filter cake and to shorten the filtration times, filter presses in which a filter plate displays a membrane which delimits the filter chamber from one side are known. Such a filter plate is referred to as a membrane filter plate. In the case of a filter press having membrane filter plates the press filtration which is initially carried out is succeeded by a compressive filtration in which the elastic membranes of the filter chambers are impinged by a pressure medium, such that said elastic membranes constrict the space in which the filter cake is situated. The filter cake is compressed in this manner, on account of which the cavities of the filter cake are decreased and on account of which the residual humidity in these cavities is further reduced.
Such a filter press is described in WO 03/095063 A1, for example. In the case of the filter press described therein, a plate stack which alternatingly displays a filter plate and a membrane filter plate is formed. The filter plate on both sides displays in each case one filter cloth which is fastened in each case in a clearance of the main body of the filter plate. The membrane filter plate on both sides displays in each case one membrane which is fastened on the main body.
In the case of this plate stack, inflow of the sludge into the filter chamber takes place via an inlet duct in the filter plate which does not comprise the membrane. This inlet duct leads from the end side of the filter plate through the plate periphery into the interior of the filter plate. There, the inlet duct terminates in a T-shaped end piece which is closed off by two inlet openings. The two inlet openings connect the inlet duct to two filter chambers which lie on averted sides of the filter plate. At the filter chamber the membrane of the membrane filter plate is disposed so as to be opposite the inlet opening, wherein the membrane in this region is configured to be planar, on account of which entry of the membrane into the inlet opening, given a sufficiently high pressure, is prevented.
Another possibility for conducting the sludge into the filter chamber is described in WO 2004/067143 A1. In this case a filling shoe is held between two filter plates between which the filter chamber is configured. A duct through which the sludge can be conducted from outside into the filter chamber is formed in the filling shoe. The filling shoe displays an outlet which is oblate on both sides and a connector which is attached thereon in an oblique manner. The filling shoe is inserted into a receptacle of one filter plate. This receptacle is adapted to the shape of the connector of the filling shoe, but displays slight play in relation thereto. The membrane of a membrane filter plate is disposed above the filling shoe. Therebelow, the filling shoe bears on the other filter plate and is supported by the latter. If the filling shoe is to be removed, the two filter plates in the filter press are moved apart. During this opening of the filter chamber the filling shoe tilts in the receptacle of the filter chamber, such that said filter shoe does not fall out. The filter shoe can readily be lifted by hand and thereafter slides out from the receptacle.
It has now emerged that in the case of arrangements in which a separate inlet part which is disposed between the filter plates is used for conducting the sludge into the filter chamber, contamination of the joints between the inlet part and the membrane may occur. Moreover, the soft membrane may be damaged by the rigid inlet part. There is furthermore the risk of the inlet duct of the inlet part being clogged, in particular if said inlet duct displays a kink. There is finally the problem of the inlet part having to be tightly received between the neighboring filter plates in order to avoid liquid leaking from the filter chamber, in particular when a very high pressure is exerted on the filter cake and the residual sludge in the filter chamber. Finally, the separate inlet part is difficult to mount.